Molecules form crystals because of the existence of intermolecular forces. The intermolecular potential energy may be expressed as a sum of nonbonded interatomic terms of the semiempirical Buckingham (exp-6-1) form: EjK equals bjbk exp(-(cj plus ck ) r jk/2) - ajaKr to the minus 6th power jk plus gj qgkr to the minus 1st power jk. This function is applied to atoms j and k (in different molecules) separated by nonbonded interatomic distance r. The present state of theory does not allow accurate calculation of the coefficients a, b, and g. The hardness parameters, c, may be estimated from theory or from compressibility data. In this research project we obtain empirical values for a, b, and q from known crystal structures. The optimum values for these nonbonded potential parameters are those which reproduce most accurately the observed crystal structures, which are referred to as the basis data. Thus, the derived nonbonded pontential energy functions may be used to understand the energetics and geometry of the packing of molecules in crystals. An important goal of the project, stated in negative terms, is that this be physically meaningful and not be merely a "curve fitting" process. If the nonbonded potential functions are physically meaningful they will be transferable to crystal structures not contained in the basis data.